Ok so I'm swapping out the 350 in my 72 for a 430. My cars an ac car. What will I need to change for the big block swap. Te guys offering the th400 for a little more cash will the th350 tranny bolt on to the 430? is it worth it or should I push the th350 a little more??
Ive done that swap. 67 430 in a 72 Skylark 350 The TH350 should bolt right up. Nothing wrong with a TH 400 either, but if oyu go TH400 youll need a gas pedal setup with the TH400 downshift switch. youll need frame pads and motor mounts. Big Block Buick radiator shroud and hoses Exhaust downpipes I think that was about it. My stock 430 felt like a tank engine - nice torque! I have it on an engine stand now, awaiting its next calling. EDIT note that I removed the AC on my car. to keep the AC you would need of course the BBB AC brackets and possibly ac lines?
You should also replace the front springs or the car will feel pretty soggy in the front end especially around corners or braking. Most people take the front suspension apart anyway to get at the frame pads bolts inside the frame which are a pain. Keeping the th350 is for sure easier in the short term, if you are not racing then it should hold up fine. If you do plan to race a lot then swap in a th400 as well but remember to modify the e-brake cable, swap the driveshaft, move the cross member and like Ken says hook up the kickdown switch.
If you can, go the th400 route! I have a TH350 behind a 430 and after a few test runs at the track the transmission was slipping. With some reinforcements like an extra clutch pack and a hardened sprag race, the th350 should handle the torque of a BBB.
